Evangelical organizers from as far away as California have been quietly mining Ohio pastors and their pews for evangelical voters, hoping to tip the election Mitt Romney’s way, just as they did for President George W. Bush in 2004.

Largely ignored by the press in the 2004 campaign, those evangelical voters became the story of that year’s election, spawning a renewed emphasis by both parties on so-called “values voters.” After a big drop in turnout in 2008, they are riding under the radar again — and Republicans say their bloc could be the deciding factor.

“In 2008, too many evangelical voters stayed home and the ‘Reagan Democrats’ stayed with Barack Obama,” said Ken Blackwell, a Republican evangelical who was the Ohio secretary of state when Mr. Bush narrowly won re-election, thanks to efforts by Mr. Blackwell and others to find and motivate Christian first-time voters in Ohio, mainly in the state’s western counties.

Mr. Blackwell predicted that evangelicals this year “will surpass their 2004 turnout for Bush, and that, coupled with the movement of Reagan Democrats away from Obama, will provide Romney a winning edge.”

In 2004, Ohio was not so much a turnout election as one marking a change in the composition of the electorate. First-time religious voters targeted by the Bush campaign also came out to vote for a state referendum against gay marriage.